In a semiconductor wafer, it is general that after mounting a circuit on its front face, in order to adjust a thickness of the wafer, the wafer back face side is subjected to grinding processing. In grinding processing of the wafer back face, a pressure sensitive adhesive sheet for protecting the circuit, which is called a back grind tape, is stuck onto the front face of the wafer.
In addition, in recent years, a semiconductor chip is sometimes produced by a so-called dicing before grinding method, in which after grooving is performed by means of dicing from the wafer front face side, the wafer back face side is ground until reaching the groove, whereby the wafer is singulated into chips (see, for example, PTL 1). According to the dicing before grinding method, it is possible to obtain an extremely thin semiconductor chip. However, the chip becomes brittle, and when the wafer is singulated into chips a breakage is generated in the four corners, etc. of the semiconductor chip, and a problem of so-called kerf shift in which chips minutely move, whereby the alignment of chips is disordered is caused.
As a back grind tape for dicing before grinding, there has hitherto been known one composed of a rigid substrate, a buffer layer provided on one face of the rigid substrate, and a pressure sensitive adhesive layer provided on the other face of the rigid substrate. In this back grind tape, by regulating a Young's modulus of the rigid substrate to 1,000 MPa or more and also regulating a maximum value of tan δ of the buffer layer to 0.5 or more, not only the chip alignment after dividing the wafer is made favorable, but also a breakage and the like as generated in the singulated semiconductor chips are reduced (see, for example, PTL 2).